[llvm] [RISCV] Add helper functions to detect CLZ/CTZ/CPOP-like support. (PR #158148)

[Craig Topper via llvm-commits]

https://github.com/topperc created https://github.com/llvm/llvm-project/pull/158148

None

>From b4024b5751077705debc87d3abe8b10164d4d5d8 Mon Sep 17 00:00:00 2001
From: Craig Topper <craig.topper at sifive.com>
Date: Thu, 11 Sep 2025 13:20:18 -0700
Subject: [PATCH] [RISCV] Add helper functions to detect CLZ/CTZ/CPOP-like
 support.

---
 llvm/lib/Target/RISCV/RISCVISelLowering.cpp | 16 ++++++++--------
 llvm/lib/Target/RISCV/RISCVSubtarget.h      | 11 +++++++++++
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 037eec05e4301..4f137756d2f48 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -403,12 +403,14 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
                        Legal);
   }
 
-  if (Subtarget.hasStdExtZbb() ||
-      (Subtarget.hasVendorXCVbitmanip() && !Subtarget.is64Bit())) {
+  if (Subtarget.hasCTZLike()) {
     if (Subtarget.is64Bit())
       setOperationAction({ISD::CTTZ, ISD::CTTZ_ZERO_UNDEF}, MVT::i32, Custom);
   } else {
     setOperationAction(ISD::CTTZ, XLenVT, Expand);
+  }
+
+  if (!Subtarget.hasCPOPLike()) {
     // TODO: These should be set to LibCall, but this currently breaks
     //   the Linux kernel build. See #101786. Lacks i128 tests, too.
     if (Subtarget.is64Bit())
@@ -418,8 +420,7 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
     setOperationAction(ISD::CTPOP, MVT::i64, Expand);
   }
 
-  if (Subtarget.hasStdExtZbb() || Subtarget.hasVendorXTHeadBb() ||
-      (Subtarget.hasVendorXCVbitmanip() && !Subtarget.is64Bit())) {
+  if (Subtarget.hasCLZLike()) {
     // We need the custom lowering to make sure that the resulting sequence
     // for the 32bit case is efficient on 64bit targets.
     // Use default promotion for i32 without Zbb.
@@ -2158,13 +2159,11 @@ bool RISCVTargetLowering::signExtendConstant(const ConstantInt *CI) const {
 }
 
 bool RISCVTargetLowering::isCheapToSpeculateCttz(Type *Ty) const {
-  return Subtarget.hasStdExtZbb() ||
-         (Subtarget.hasVendorXCVbitmanip() && !Subtarget.is64Bit());
+  return Subtarget.hasCTZLike();
 }
 
 bool RISCVTargetLowering::isCheapToSpeculateCtlz(Type *Ty) const {
-  return Subtarget.hasStdExtZbb() || Subtarget.hasVendorXTHeadBb() ||
-         (Subtarget.hasVendorXCVbitmanip() && !Subtarget.is64Bit());
+  return Subtarget.hasCLZLike();
 }
 
 bool RISCVTargetLowering::isMaskAndCmp0FoldingBeneficial(
@@ -24843,6 +24842,7 @@ bool RISCVTargetLowering::isCtpopFast(EVT VT) const {
     return isTypeLegal(VT) && Subtarget.hasStdExtZvbb();
   if (VT.isFixedLengthVector() && Subtarget.hasStdExtZvbb())
     return true;
+  // FIXME: Should use hasCPOPLike here.
   return Subtarget.hasStdExtZbb() &&
          (VT == MVT::i32 || VT == MVT::i64 || VT.isFixedLengthVector());
 }
diff --git a/llvm/lib/Target/RISCV/RISCVSubtarget.h b/llvm/lib/Target/RISCV/RISCVSubtarget.h
index 50e76df56e575..0d9cd16a77937 100644
--- a/llvm/lib/Target/RISCV/RISCVSubtarget.h
+++ b/llvm/lib/Target/RISCV/RISCVSubtarget.h
@@ -186,6 +186,17 @@ class RISCVSubtarget : public RISCVGenSubtargetInfo {
     return HasStdExtZfhmin || HasStdExtZfbfmin;
   }
 
+  bool hasCLZLike() const {
+    return HasStdExtZbb || HasVendorXTHeadBb ||
+           (HasVendorXCVbitmanip && !IsRV64);
+  }
+  bool hasCTZLike() const {
+    return HasStdExtZbb || (HasVendorXCVbitmanip && !IsRV64);
+  }
+  bool hasCPOPLike() const {
+    return HasStdExtZbb || (HasVendorXCVbitmanip && !IsRV64);
+  }
+
   bool hasBEXTILike() const { return HasStdExtZbs || HasVendorXTHeadBs; }
 
   bool hasCZEROLike() const {